Abstract: The present invention is related to a mechanism for guaging the expansion of a trawl net in correspondence with the number of fish caught within the trawl. The mechanism includes sensors adapted to be fastened to the masks of the trawl net in order to sense changes in the geometry of the mask. Each sensor includes a permanent magnet and a reed contact disposed to be activated by the magent as a result of a predetermined trawl net expansion, thereby transmitting a signal indicative of such expansion to a detection and indication mechanism located on board an associated trawler.

Abstract: A method and means for recording auxiliary information, e.g. temperature readings, on echo sounder recorders or similar display devices, in addition to the normal recording, said information being presented as the distance of a recorded mark from a point of reference. In order to always secure a clear representation of such information, according to the invention the normal record on the display is blanked out or reduced in intensity adjacent said mark.